Configure NS16550 transmission format settings on initialization on PCs.
Currently, the NS116550 serial line controller is left with its
settings as it was left by the boot firmware and/or bootloader.
On my computer, this was an invalid configuration, and it left me
with a really slow booting system, since each output character
had to go through the full timeout loop in ns16550_sendb().
This patch adds the necessary bit and register descriptions to configure
the baud rate and transmission settings, as well as configuring them on
post-SMP initialization on ia32 and amd64, currently with values matching
the ns8250 userspace character device driver (38400 baud, 8-bit words,
2 stop bits, no parity).
This could perhaps be changed to be adjustable with a kernel command-line
argument, or through the configuration system.
This change does not affect emulators, since those largely ignore these
settings.
